In the field of arc welding, the three (3) main types of arc welding are submerged arc welding (SAW), shielded metal arc welding (SMAW), and flux-cored arc welding (FCAW). In submerged arc welding, coalescence is produced by heating with an electric arc between a bare-metal electrode and the metal being worked. The welding is blanketed with a granular or fusible material or flux. The welding operation is started by striking an arc beneath the flux to produce heat to melt the surrounding flux so that it forms a subsurface conductive pool which is kept fluid by the continuous flow of current. The end of the electrode and the workpiece directly below it becomes molten, and molten filler metal is deposited from the electrode onto the work. The molten filler metal displaces the flux pool and forms the weld. In shielded metal arc welding, shielding is produced by a flux coating instead of a loose granular blanket of flux. In flux-cored electrodes, the flux is contained within the metal sheath.
In the art of welding, much prior effort has been expended in developing flux compositions of the type having predetermined flux components intended to perform in predetermined manners. A large number of compositions have been developed for use as fluxes in arc welding both for use generally as welding fluxes and for use as a coating on a metallic core or within a sheath. Fluxes are utilized in arc welding to control the arc stability, modify the weld metal composition, and provide protection from atmospheric contamination. Arc stability is commonly controlled by modifying the composition of the flux. It is therefore desirable to have substances which function well as plasma charge carriers in the flux mixture. Fluxes also modify the weld metal composition by rendering impurities in the metal more easily fusible and providing substances with which these impurities may combine, in preference to the metal to form slag. Other materials may be added to lower the slag melting point, to improve slag fluidity, and to serve as binders for the flux particles.
Coated electrodes and cored electrodes are commonly used in electric arc welding of steel base metals. These electrodes generally yield high strength welds in a single pass and multiple passes at high welding speeds. These electrodes are formulated to provide a solid, substantially nonporous weld bead with tensile strength, ductility and impact strength to meet the desired end use of various applications. The electrodes are also formulated to minimize the qualities of slag generated during a welding procedure. The slag after the welding procedure is removed to provide a clean surface that, if desired, can be later treated (e.g., painted, coated) to enhance appearance, inhibit corrosion, etc.
Cored electrodes are used increasingly as an alternative to solid weld wires for improved productivity in structural fabrication. Cored electrodes have a metal sheath and a core containing a composition of various materials. Cored electrodes typically provide increased weld deposition rates and produce wider and more consistent penetration profiles than many solid wires. Cored electrodes also typically generate less fumes and spatter, provide improved arc stability and produce weld deposits with improved wetting characteristics in comparison to many solid wires.
One type of welding operation that has presented many challenges is the welding of dissimilar metals. Due to the different compositions of the metals, the weld formed between these two metals is exposed to great stresses commonly resulting in the formation of cracks. These stresses are due in part to the different physical properties of the metals (e.g.; coefficient of thermal expansion, thermal conductivity, hardenability, yield strength, elongation, etc.). Another type of welding operation that presents challenges is the hardfacing of carbon steel and low alloy steel with chromium carbide. Cracks commonly form in such hardfacing operations due to hydrogen diffusing into the high carbon steel during the hardfacing operation and also due to cracks forming in the chromium carbide that propagate into the high carbon steel
In view of the present state of the art of welding dissimilar metals and hardfacing carbon steel and low alloy steel, there is a need for a welding electrode that can be used to reduce the incidence of cracking in such welding and hardfacing procedures.